A historical literature review of coronary microvascular obstruction and intra-myocardial hemorrhage as functional/structural phenomena

The analysis of experimental data demonstrates that platelets and neutrophils are involved in the no-reflow phenomenon, also known as microvascular obstruction (MVO). However, studies performed in the isolated perfused hearts subjected to ischemia/reperfusion (I/R) do not suggest the involvement of microembolization and microthrombi in this phenomenon. The intracoronary administration of alteplase has been found to have no effect on the occurrence of MVO in patients with acute myocardial infarction. Consequently, the major events preceding the appearance of MVO in coronary arteries are independent of microthrombi, platelets, and neutrophils. Endothelial cells appear to be the target where ischemia can disrupt the endothelium-dependent vasodilation of coronary arteries. However, reperfusion triggers more pronounced damage, possibly mediated by pyroptosis. MVO and intra-myocardial hemorrhage contribute to the adverse post-infarction myocardial remodeling. Therefore, pharmacological agents used to treat MVO should prevent endothelial injury and induce relaxation of smooth muscles. Ischemic conditioning protocols have been shown to prevent MVO, with L-type Ca ²⁺ channel blockers appearing the most effective in treating MVO.

The Role of Mitochondrial KATP Channels in the Infarct-Reducing Effect of Normobaric Hypoxia

We studied the role of K_ATP channels in the infarct-limiting effect of short-term normobaric hypoxia. Male Wistar rats were subjected to a 45-min coronary artery occlusion followed by a 120-min reperfusion. Normobaric hypoxia was simulated 30 min before coronary artery occlusion: 6 sessions of hypoxia (8% O₂, 10 min) and reoxygenation (21% O₂, 10 min). The following drugs were administered to rats: glibenclamide, 5-hydroxydecanoate, and HMR1098. It was found that normobaric hypoxia contributes to a decrease in myocardial infarct size by 36%. Preliminary administration of glibenclamide or 5-hydroxydecanoate eliminated the infarct-reducing effect of normobaric hypoxia. Activator of mitochondrial K_ATP channel diazoxide limited the infarct size. These findings suggest that mitochondrial K_ATP channels are involved into the cardioprotective effect of normobaric hypoxia.

SPARC, a Novel Regulator of Vascular Cell Function in Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension (PH) is a life-threatening disease, characterized by excessive pulmonary vascular remodeling, leading to elevated pulmonary arterial pressure and right heart hypertrophy. PH can be caused by chronic hypoxia, leading to hyper-proliferation of pulmonary arterial smooth muscle cells (PASMCs) and apoptosis-resistant pulmonary microvascular endothelial cells (PMVECs). On reexposure to normoxia, chronic hypoxia-induced PH in mice is reversible. In this study, the authors aim to identify novel candidate genes involved in pulmonary vascular remodeling specifically in the pulmonary vasculature.

METHODS

After microarray analysis, the authors assessed the role of SPARC (secreted protein acidic and rich in cysteine) in PH using lung tissue from idiopathic pulmonary arterial hypertension (IPAH) patients, as well as from chronically hypoxic mice. In vitro studies were conducted in primary human PASMCs and PMVECs. In vivo function of SPARC was proven in chronic hypoxia-induced PH in mice by using an adeno-associated virus-mediated Sparc knockdown approach.

RESULTS

C57BL/6J mice were exposed to normoxia, chronic hypoxia, or chronic hypoxia with subsequent reexposure to normoxia for different time points. Microarray analysis of the pulmonary vascular compartment after laser microdissection identified Sparc as one of the genes downregulated at all reoxygenation time points investigated. Intriguingly, SPARC was vice versa upregulated in lungs during development of hypoxia-induced PH in mice as well as in IPAH, although SPARC plasma levels were not elevated in PH. TGF-β1 (transforming growth factor β1) or HIF2A (hypoxia-inducible factor 2A) signaling pathways induced SPARC expression in human PASMCs. In loss of function studies, SPARC silencing enhanced apoptosis and reduced proliferation. In gain of function studies, elevated SPARC levels induced PASMCs, but not PMVECs, proliferation. Coculture and conditioned medium experiments revealed that PMVECs-secreted SPARC acts as a paracrine factor triggering PASMCs proliferation. Contrary to the authors' expectations, in vivo congenital Sparc knockout mice were not protected from hypoxia-induced PH, most probably because of counter-regulatory proproliferative signaling. However, adeno-associated virus-mediated Sparc knockdown in adult mice significantly improved hemodynamic and cardiac function in PH mice.

CONCLUSIONS

This study provides evidence for the involvement of SPARC in the pathogenesis of human PH and chronic hypoxia-induced PH in mice, most likely by affecting vascular cell function.

Right Ventricular Response to Acute Hypoxia Exposure: A Systematic Review

Background: Acute hypoxia exposure is associated with an elevation of pulmonary artery pressure (PAP), resulting in an increased hemodynamic load on the right ventricle (RV). In addition, hypoxia may exert direct effects on the RV. However, the RV responses to such challenges are not fully characterized. The aim of this systematic review was to describe the effects of acute hypoxia on the RV in healthy lowland adults.

Methods: We systematically reviewed PubMed and Web of Science and article references from 2005 until May 2021 for prospective studies evaluating echocardiographic RV function and morphology in healthy lowland adults at sea level and upon exposure to simulated altitude or high-altitude.

Results: We included 37 studies in this systematic review, 12 of which used simulated altitude and 25 were conducted in high-altitude field conditions. Eligible studies reported at least one of the RV variables, which were all based on transthoracic echocardiography assessing RV systolic and diastolic function and RV morphology. The design of these studies significantly differed in terms of mode of ascent to high-altitude, altitude level, duration of high-altitude stay, and timing of measurements. In the majority of the studies, echocardiographic examinations were performed within the first 10 days of high-altitude induction. Studies also differed widely by selectively reporting only a part of multiple RV parameters. Despite consistent increase in PAP documented in all studies, reports on the changes of RV function and morphology greatly differed between studies.

Conclusion: This systematic review revealed that the study reports on the effects of acute hypoxia on the RV are controversial and inconclusive. This may be the result of significantly different study designs, non-compliance with international guidelines on RV function assessment and limited statistical power due to small sample sizes. Moreover, the potential impact of other factors such as gender, age, ethnicity, physical activity, mode of ascent and environmental factors such as temperature and humidity on RV responses to hypoxia remained unexplored. Thus, this comprehensive overview will promote reproducible research with improved study designs and methods for the future large-scale prospective studies, which eventually may provide important insights into the RV response to acute hypoxia exposure.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

An Exaggerated Rise in Pulmonary Artery Pressure in a High-Altitude Dweller during the Cold Season

Chronic hypoxia-induced sustained pulmonary vasoconstriction and vascular remodeling lead to mild-to-moderate elevation of pulmonary artery pressure in high-altitude residents. However, in some of them, severe pulmonary hypertension may develop. Besides hypoxia, high-altitude residents also face other environmental challenges such as low ambient temperatures. We describe a case of a 49-year-old woman of Kyrgyz ethnicity with abnormally increased pulmonary artery pressure, revealed by Doppler echocardiography. Significantly elevated pulmonary artery pressure was detected in late winter and this was not associated with right ventricular hypertrophy or right ventricular dysfunction. Repeat echocardiography performed in late summer disclosed a significant attenuation of pulmonary artery pressure elevation, with no changes in right ventricular performance parameters. This case illustrates that, in susceptible individuals, long-term cold exposure could induce an abnormal pulmonary artery pressure rise, which can be reversed during warm seasons as in our patient. In certain circumstances, however, additional factors could contribute to a sustained pulmonary artery pressure increase and the development of persistent pulmonary hypertension, which often leads to right heart failure and premature death.

Cardiac Acclimatization at High Altitude in Two Different Ethnicity Groups

Gaur, Priya, Meerim Sartmyrzaeva, Abdirashit Maripov, Kubatbek Muratali Uulu, Supriya Saini, Koushik Ray, Krishna Kishore, Almaz Akunov, Akpay Sarybaev, Bhuvnesh Kumar, Shashi Bala Singh, and Praveen Vats. Cardiac acclimatization at high altitude in two different ethnicity groups. High Alt Med Biol. 22:58-69, 2021. Introduction: High altitude (HA) exposure causes substantial increase in pulmonary artery pressure (PAP) and resistance. However, the effects of HA hypoxia exposure on cardiac function remain incompletely understood. Studies evaluating interethnic differences in cardiac functions in response to HA exposure are lacking. We aimed to compare the cardiac performance in Indian versus Kyrgyz healthy lowland subjects over the course of a 3-week HA exposure at 4,111 m. Methodology: Ten Indians and 20 Kyrgyz subjects were studied to assess cardiac acclimatization noninvasively by echocardiography in two different ethnic groups for 3 weeks of stay at HA. Pulmonary hemodynamics, right and left ventricular functions were evaluated at basal and on days 3, 7, 14, and 21 of HA exposure and on day 3 of deinduction. Results: HA exposure significantly increased PAP, pulmonary vascular resistance, cardiac output (CO), and heart rates (HRs) in both groups. Tricuspid regurgitant gradient increased significantly in both the group at day 3 versus basal; 38.9 mmHg (31.8, 42.9) versus 21.9 mmHg (19.5, 22.6) in Kyrgyz; and 34.1 mmHg (30.2, 38.5) versus 20.4 mmHg (19.7, 21.3) in Indians. HR increased significantly in Indians at day 3 and 7, whereas in Kyrgyz throughout exposure. CO increased significantly in both groups at day 3 versus basal with 5.9 L/min (5.5, 6.4) versus 5.1 L/min (4.4, 5.9) in Kyrgyz, and 5.7 L/min (5.56, 5.98) versus 4.9 L/min (4.1, 5.3) in Indians. Both groups exhibited preserved right ventricular diastolic and systolic functions at HAs. HA exposure changed the left ventricular diastolic parameters only in Kyrgyz subjects with impaired mitral inflow E/A, but not in Indian subjects. All cardiac changes induced at HAs have been recovered fully upon deinduction in both, except lateral-septal A', which remained low in Indians. Conclusion: Although pulmonary hemodynamics responses were similar in both groups, there were differences in cardiac functional parameters between the two in response to HA exposure that may be accounted to ethnic variation.

Reversal of Pulmonary Hypertension in a Patient with Chronic Mountain Sickness after Relocation to Low Altitude

Long-term high altitude residence can be complicated by development of Chronic Mountain Sickness (CMS) characterised by excessive erythrocytosis and neurological symptoms. In some patients, CMS may be associated with various degrees of Pulmonary Hypertension (PH). There have been no reports on changes in the pulmonary circulation and Right Ventricular (RV) structure following translocation to low altitude of patients with CMS. Here the authors report a case of 56 years old female patient, resident of Sary Mogol (3,000 m, Kyrgyzstan), diagnosed of CMS on clinical and laboratory examination. Transthoracic echocardiography revealed slightly dilated Right ventricle and significantly enlarged Pulmonary Artery diameter was found. The patient undergone complete resolution of symptoms and alleviation of PH within three years of residence at low altitude. Thus, relocation to low altitude cures CMS and reverses PH.

Temporal transcriptome analysis suggest modulation of multiple pathways and gene network involved in cell-cell interaction during early phase of high altitude exposure

High altitude (HA) conditions induce several physiological and molecular changes, prevalent in individuals who are unexposed to this environment. Individuals exposed towards HA hypoxia yields physiological and molecular orchestration to maintain adequate tissue oxygen delivery and supply at altitude. This study aimed to understand the temporal changes at altitude of 4,111m. Physiological parameters and transcriptome study was conducted at high altitude day 3, 7, 14 and 21. We observed changes in differentially expressed gene (DEG) at high altitude time points along with altered BP, HR, SpO2, mPAP. Physiological changes and unsupervised learning of DEG's discloses high altitude day 3 as distinct time point. Gene enrichment analysis of ontologies and pathways indicate cellular dynamics and immune response involvement in early day exposure and later stable response. Major clustering of genes involved in cellular dynamics deployed into broad categories: cell-cell interaction, blood signaling, coagulation system, and cellular process. Our data reveals genes and pathways perturbed for conditions like vascular remodeling, cellular homeostasis. In this study we found the nodal point of the gene interactive network and candidate gene controlling many cellular interactive pathways VIM, CORO1A, CD37, STMN1, RHOC, PDE7B, NELL1, NRP1 and TAGLN and the most significant among them i.e. VIM gene was identified as top hub gene. This study suggests a unique physiological and molecular perturbation likely to play a critical role in high altitude associated pathophysiological condition during early exposure compared to later time points.

Pulmonary Vascular Pressure Response to Acute Cold Exposure in Kyrgyz Highlanders

Background/Aims: Long-term high altitude residence leads to a sustained increase in pulmonary vascular resistance and elevation of pulmonary artery pressure due to chronic alveolar hypoxia. However, living at high altitude is also associated with other environmental factors such as cold. There is still little experimental evidence suggesting detrimental effects of low temperatures on the pulmonary vasculature. Therefore, our objective was to investigate acute effects of cold exposure on the pulmonary circulation in Kyrgyz high altitude natives. Methods: Responses of the pulmonary circulation during acute exposure to controlled cold conditions (4°C-6°C) for 60 minutes were measured in highlanders using Doppler echocardiography. Based on the Doppler echocardiography-derived tricuspid regurgitant systolic pressure gradient (TRG), subjects with TRG ≥40 mmHg were allocated into the pulmonary hypertension (PH) group. Participants from the PH group were compared with volunteer control subjects with TRG <40 mmHg. All baseline measurements were evaluated in a warm room during 60 minutes (22°C-28°C). Following baseline echocardiography, the subjects were assigned to either warm or cold exposure for an additional 60 minutes. Results: Acute cold exposure significantly increased TRG both in the control (ΔTRG, 4.93 mmHg) and in the PH (ΔTRG, 8.15 mmHg) group, compared to the respective warm exposure conditions (ΔTRG, -0.14 and -0.05 mmHg). No changes in cardiac output were observed upon cold exposure. Conclusion: Thus, acute exposure to cold leads to elevation of pulmonary artery pressure in high altitude residents.

A Case of Chronic Thromboembolic Pulmonary Hypertension in a High-Altitude Dweller

Chronic hypoxia causes sustained pulmonary vasoconstriction and vascular remodeling leading to development of pulmonary hypertension in high-altitude residents. Although pulmonary hypertension is of mild to moderate degrees in most cases, some high-altitude residents may develop severe pulmonary hypertension. We report a case of a 47-year-old female highlander of Kyrgyz ethnicity who presented with exertional breathlessness and echocardiographic signs of severe pulmonary hypertension, who was diagnosed as having chronic thromboembolic pulmonary hypertension (CTEPH). To the best of our knowledge, this is the first documented case of severe CTEPH in a high-altitude dweller. This case illustrates that causes other than hypoxia may underlie and/or contribute to severe pulmonary hypertension in residents of high altitude.

A Temporal Study on Learning and Memory at High Altitude in Two Ethnic Groups

Introduction: Cognitive function has been compromised during high-altitude (HA) exposure due to slowing of mental processing. Materials and Methods: A total of 20 Indian and 20 Kyrgyz soldiers were studied at 4111 m to assess cognitive function in two different ethnic groups. Paired associate learning, pattern recognition memory, spatial span (SSP), spatial working memory (SWM), choice reaction time (CRT), and simple reaction time (SRT) were evaluated at sea level and on days 3, 7, 14, and 21 of HA stay and on day 3 of deinduction. Results: All the parameters were significantly affected at HA. Indian soldiers were acclimatized by 7 days but Kyrgyz soldiers required 21 days for acclimatization. A slow impairment in SWM, CRT, and SRT was observed in Kyrgyz soldiers than in Indian soldiers and it continues throughout 21 days of HA stay, but for Indian soldiers the deterioration was maximum on day 7 and improvement in SWM, CRT, and SRT was observed on day 14 and close to baseline value on day 21. After deinduction, although Indian soldiers attained the normal value, Kyrgyz soldiers had higher value than baseline in SSP, SWM, CRT, and SRT. Conclusion: Difference in the cognitive performances of Indian and Kyrgyz soldiers may be due to the ethnogenetic diversity of these two groups.

Circulating Apoptotic Signals During Acute and Chronic Exposure to High Altitude in Kyrgyz Population

Background: Circulating apoptotic signals (CASs) have been described in the pathologies associated with dysregulated apoptosis, such as cancer, heart diseases, and pulmonary hypertension (PH). However, nothing is known about the expression profiles of these markers in the circulation of humans exposed to acute and chronic effects of high altitude (HA). Methods: Gene expression levels of different apoptotic signals (ASs) were analyzed in human pulmonary artery smooth muscle cells (PASMCs) upon hypoxia incubation. In addition, we measured the plasma values of relevant CAS in Kyrgyz volunteers during acute and chronic exposure to HA. Finally, we analyzed the effects of pro-apoptotic mediator Fas ligand (FasL) on apoptosis and proliferation of human PASMCs. Results: Several cellular AS were increased in PASMCs exposed to hypoxia, in comparison to normoxia condition. Among analyzed CAS, there was a prominent reduction of FasL in lowlanders exposed to HA environment. Furthermore, decreased circulatory levels of FasL were found in highlanders with HA-induced PH (HAPH), as compared to the lowland controls. Furthermore, FasL concentration in plasma negatively correlated with tricuspid regurgitant gradient values. Finally, FasL exerted pro-apoptotic and anti-proliferative effects on PASMCs. Conclusion: Our data demonstrated that circulating levels of FasL are reduced during acute and chronic exposure to HA environment. In addition, dysregulated FasL may play a role in the context of HAPH due to its relevant functions on apoptosis and proliferation of PASMCs.

Hemoglobin Changes After Long-Term Intermittent Work at High Altitude

Chronic high altitude hypoxia leads to an increase in red cell numbers and hemoglobin concentration. However, the effects of long-term intermittent hypoxia on hemoglobin concentration have not fully been studied. The aim of this study was to evaluate hemoglobin levels in workers commuting between an elevation of 3,800 m (2-week working shift) and lowland below 1,700 m (2 weeks of holiday). A total of 266 healthy males, aged from 20 to 69 years (mean age 45.9 ± 0.6 years), were included into this study. The duration of intermittent high altitude exposure ranged from 0 to 21 years. Any cardiac or pulmonary disorder was excluded during annual check-ups including clinical examination, clinical lab work (blood cell count, urine analysis, and biochemistry), ECG, echocardiography, and pulmonary function tests. The mean hemoglobin level in workers was 16.2 ± 0.11 g/dL. Univariate linear regression revealed an association of the hemoglobin levels with the years of exposure. Hemoglobin levels increased 0.068 g/dL [95% CI: 0.037 to 0.099, p < 0.001] for every year of intermittent high altitude exposure. Further, after adjusting for other confounding variables (age, living at low or moderate altitude, body mass index, and occupation) using multivariable regression analysis, the magnitude of hemoglobin level changes decreased, but remained statistically significant: 0.046 g/dL [95% CI: 0.005 to 0.086, p < 0.05]. Besides that, a weak linear relationship between hemoglobin levels and body mass index was revealed, which was independent of the years of exposure to high altitude (0.065 g/dL [95% CI: 0.006 to 0.124, p < 0.05]). We concluded that hemoglobin levels have a linear relationship with the exposure years spent in intermittent hypoxia and body mass index.

Global expression profiling and pathway analysis in two different population groups in relation to high altitude

High altitude (HA) is associated with number of stresses. Response of these stresses may vary in different populations depending upon altitude, duration of residency, ancestry, geographical variation, lifestyle, and ethnicities. For understanding population variability in transcriptome, array-based global gene expression profiling was performed on extracted RNA of male volunteers of two different lowland population groups, i.e., Indians and Kyrgyz, at baseline and day 7 of HA exposure (3200 m). A total of 97 genes were differentially expressed at basal in Kyrgyz as compared to Indians (82 downregulated and 15 upregulated), and 196 were differentially expressed on day 7 of HA (118 downregulated and 78 upregulated). Ingenuity Pathway Analysis and gene ontology highlighted eIF2 signaling with most significant negative activation z score at basal in Kyrgyz compared to Indians with downregulation of various L- and S-ribosomal proteins indicating marked translational repression. On day 7, cAMP-mediated signaling is most enriched with positive activation z score in Kyrgyz compared to Indians. Plasma cAMP levels were higher in Kyrgyz on day 7 compared to Indians. Extracellular adenosine levels were elevated in both the groups upon HA, but higher in Kyrgyz compared to Indians. Valedictory qRT-PCR showed upregulation of ADORA2B and CD73 along with downregulation of ENTs in Kyrgyz compared to Indians indicating elevated levels of extracellular nucleotides mainly adenosine and activation of extracellular cAMP-adenosine pathway which as per literature triggers endogenous protective mechanisms under stress conditions like hypoxia. Thus, transcriptome changes at HA are population-specific, and it may be necessary to take care while interposing similar results in different populations.

A Case of Subacute Infantile Mountain Sickness in a Kyrgyz Child

Muratali Uulu, Kubatbek, Meerim Cholponbaeva, Melis Duishobaev, Aidana Toktosunova, Abdirashit Maripov, Akylbek Sydykov, and Akpay Sarybaev. A case of subacute infantile mountain sickness in a Kyrgyz child. High Alt Med Biol. 19:208-210, 2018.-Subacute infantile mountain sickness (SIMS) is a syndrome of severe pulmonary hypertension and right heart failure that develops in infants born in the lowlands and subsequently brought to live at high altitudes. Earlier postmortem studies have demonstrated significant remodeling of small pulmonary arteries as well as right ventricular hypertrophy and dilatation. In this report, we present a case of SIMS in a Kyrgyz child born to a native highlander mother evaluated by conventional echocardiography and tissue Doppler imaging. An echocardiogram showed severe pulmonary hypertension, a markedly dilated right ventricle with flattening of interventricular septum, and right ventricular dysfunction. To our knowledge, this is the first report of noninvasive imaging of pulmonary circulation and right ventricle in an infant with SIMS and confirmed the diagnosis using echocardiography.

Acclimatization to High Altitude in the Tien Shan: A Comparative Study of Indians and Kyrgyzis

OBJECTIVE

To study the changes in pulmonary function of human male volunteers from 2 different populations: Indians and Kyrgyzis before and after ascent to 3,200 m and during a 4-week stay at that altitude.

METHODS

Ten healthy soldiers of the Indian army (22-25 years of age) and 10 Kyrgyzis recruits (19-20 years of age), height and weight matched, were volunteers in this study. Their pulmonary functions were evaluated at baseline (Bishkek, 760 m); on days 2, 13, and 25 at a mountain clinic at Tuya Ashuu pass (3,200 m) in the northern Tien Shan Range; and on return to Bishkek. A dry spirometer was used to measure lung function at each location.

RESULTS

Results indicated that Kyrgyzis had significantly larger forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV(1)) than those of the Indians, but their peak expiratory flow rate (PEF), forced expiratory flow rate at 25% to 75% of FVC (FEF(25-75%)), and maximal voluntary ventilation (MVV) measures were comparable. At high altitude (HA), FVC showed significant reduction on day 2, with subsequent recovery in the Kyrgyzis; but in the Indians, FVC showed gradual reduction, and on day 25, it was significantly reduced compared with the baseline value. FEV(1) did not show any change with altitude in either group. Expiratory flow rates and MVV showed significantly higher values at HA in both groups. However, after air density correction for the 2 altitudes, PEF and MVV showed no changes from their baseline values, and the mid-expiratory flow rate (FEF(25-75%)) was actually reduced in both groups: on day 2 in the Kyrgyzis and on day 25 in the Indians. On day 2 of return from a 4-week stay at HA, all test measures were back to their baseline values.

CONCLUSIONS

The major difference between the 2 populations was larger lung volumes in the Kyrgyzis compared with the Indians, with no differences seen in their flow rate measures. Also, there was a different time schedule of altitude-induced reductions in FVC and FEF(25-75%).

Serial changes in nasal potential difference and lung electrical impedance tomography at high altitude

Recent work suggests that treatment with inhaled beta(2)-agonists reduces the incidence of high-altitude pulmonary edema in susceptible subjects by increasing respiratory epithelial sodium transport. We estimated respiratory epithelial ion transport by transepithelial nasal potential difference (NPD) measurements in 20 normal male subjects before, during, and after a stay at 3,800 m. NPD hyperpolarized on ascent to 3,800 m (P < 0.05), but the change in potential difference with superperfusion of amiloride or isoprenaline was unaffected. Vital capacity (VC) fell on ascent to 3,800 m (P < 0.05), as did the normalized change in electrical impedance (NCI) measured over the right lung parenchyma (P < 0.05) suggestive of an increase in extravascular lung water. Echo-Doppler-estimated pulmonary artery pressure increases were insufficient to cause clinical pulmonary edema. There was a positive correlation between VC and NCI (R(2) = 0.633) and between NPD and both VC and NCI (R(2) = 0.267 and 0.418). These changes suggest that altered respiratory epithelial ion transport might play a role in the development of subclinical pulmonary edema at high altitude in normal subjects.